1. Field of the Invention
The present invention relates to an optical fiber coating applicator for applying resin coating onto an optical fiber, and particularly relates to a resin coating applicator for optical fibers, which is easy in maintenance.
2. Description of the Related Art
Conventionally, in manufacturing an optical fiber, a preform is heated and pulled so as to draw an optical fiber, and then the surrounding of the optical fiber is coated with resin or the like, cured by a curing apparatus, and wound up on a winding machine through a capstan, a pulley and so on. As the means for coating an optical fiber with resin, that which uses a nipple and a coating die is known. A coating applicator using a nipple and two coating dies for applying two coating layers is disclosed in Japanese Patent Unexamined Publication No. Hei-4-280839. Such an applicator for applying two coating layers by using two coating dies is also called a dual die. In addition, a coating applicator in which hot water is circulated around a coating die in order to control temperature of resin during application is disclosed in Japanese Patent Examined Publication No. Hei-6-55989.
In such a coating applicator, when resin grounds or rubbish foreign bodies exist in a coating die, the flow of resin is disturbed to cause deterioration in coating concentricity or cause a change in coating diameter. It is therefore preferable to regard a predetermined length of drawing as a batch, and cleaning/cleansing is performed whenever one batch is ended. In addition, preferably, the cleaning/cleansing of the coating die in every drawing batch is performed after the coating die is removed from the drawing machine and disassembled, for the resin path in the coating die is so complicated that it cannot be cleaned up if it is not disassembled. If it is disassembled, it can be cleaned up by ultrasonic cleaning with a solvent.
However, in the above-mentioned coating applicator disclosed in Japanese Patent Unexamined Publication No. Hei-4-280839, when removing and cleansing are performed every time, there is a problem that the coating die cannot be set in a pass line with high reproducibility in positioning accuracy because positioning and so on in attachment is left out of consideration. In addition, because the nipple is tapered so as to be fitted to the die holder, there is another problem that the gap between the nipple and the coating die cannot be managed accurately. In addition, because a first cylindrical coating die 27 has a structure that the concentricity is controlled by threads, there is a further problem that the control is not easy.
On the other hand, in the coating applicator disclosed in Japanese Patent Post-Examination No. Hei-6-55989, such a structure has been adopted that temperature can be controlled by the circulation of hot water, but removing from a pass line or cleaning/cleansing is left out of consideration.
As a result of further examination, it is found that the coating applicator disclosed in Japanese Patent Unexamined Publication No. Hei-4-280839 is removed while it is being disassembled, and attached to a pass line while it is being assembled, so long as viewed from the drawings, though a removal or attachment structure is not clearly described. In assembling, the coating applicator seems to be a system of fitting into a recess portion. If it is regarded as a simple fitting type, a clearance should be produced, so that it is difficult to install the coating applicator with high reproducibility even in its tilt and/or horizontal position. A resin introduction pipe is connected to the coating die, so that it is difficult on structure to reproduce the accuracy of the attachment tilt angle in the order of a few minutes because of its weight. Even if it is fixed by a thread, it is difficult to realize such an accuracy.
As for a circumferentially positioning mechanism disclosed in Japanese Patent Unexamined Publication No. Hei-4-280839, the reproducibility in attachment accuracy is left out of consideration. In addition, in a fitting structure where the outer circumferential surface of a nipple is tapered, its axial position with the upper surface of a cylindrical coating die laid under the nipple cannot be made accurate. As for the gap between the nipple and the coating die, therefore, there has not been shown a structure in which the gap between the nipple and the coating die can be defined accurately.
As has been described above, in conventional coating applicators, there is required such a working that a screw must be released to remove and clean a coating die whenever cleaning/cleansing working is performed, and at the time of assembling the screw must be fastened while making alignment. This working is not so easy.